To do this, turn on Fitness mode from the main menu. If you have PlayFit, all your requisite details will be used for the tracking. Depending on the songs you use, your height and weight, you may need between 5 and 20 songs to reach 100 calories burned.
Note: PlayFit has an achievement for burning 10,000 calories, and by the time you have ground out the 10,000 Nice and Flawless moves, you will probably have at least 2,000 calories burned, depending on your skill and weight getting you much closer to that achievement. Playfit can be downloaded from the app menu on the XBox Dashboard.